Question

cos 340o.cos 40o+sin200o.sin140o​

Answer 1

Answer:

1/2

Step-by-step explanation:

cos 340 . cos 40 + sin 200 . sin 140

• cos 340= cos (360-20) = cos20

• sin 200 = sin (180+20) = -sin20

• sin 140 = sin (180-40) = sin40]

= cos (360-20) . cos 40 + sin (180+20) . sin (180-40)

= cos 20 . cos 40 + (-sin 20) . sin 40

= cos 20 . cos 40 - sin 20 . sin 40

• cos (A+B) = cos A . cos B - sin A . sin B  

= cos (20+40)

= cos 60

= 1/2 or 0.5